We propose to obtain a more basic understanding of disorders of hearing and speech by pursuing five closely related neurobiological and behavioral studies. Project 1 deals with physiological correlates of certain auditory perceptual phenomena. Using the cat as a model, the project tests hypotheses proposed to account for intensity coding, examines the physiological bases of frequency-specific auditory brainstem response (ABR) masking techniques, and investigates CNS processing of speech and perceptually-relevant complex tones. Project II deals with ABR and behavioral measures of peripheral auditory function in humans with an emphasis on issues related to fitting children with hearing aids. This work includes human ABR studies, related psychophysical studies in adults and children, and studies of speech perception through simulated compression hearing aids. Project III deals with neural mechanisms of orofacial and laryngeal control, again using cat as a model. This work includes studies of motor cortical representation of perioral and facial musculature, anatomical and physiological studies of laryngeal innervation and control, and bulbar and suprabulbar modulation of perioral reflexes elicited by mechanical stimuli. Project IV deals with quantitative measures of vocal tract function that are applicable in clinical studies of speech disorders. This work includes studies of fine force control and evoked perioral muscle response, perioral mechano-sensitivity, and trigeminal somatosensory evoked potentials. Project V deals with the genetics of sensorineural hearing loss, applying recombinant DNA marker techniques in an effort to localize the genes for autosomal dominant hearing losses such as those associated with Waardenburg and Usher syndromes. The common goal of these studies is to improve the diagnosis and treatment of communication disorders in children by relating quantitative measures of human hearing and speech to underlying neurobiological function.